Bone screw, particularly for use with external fixators in fracture stabilization

ABSTRACT

The invention relates to a bone screw, particularly for use with external splints in fracture stabilization, comprising an elongate cylindrical body ( 2 ) of predetermined length and diameter tapering into a threaded end portion ( 5 ) which terminates with a tip ( 6 ), and an opposite screw-handling end ( 3 ). The screw-handling end ( 3 ) has substantially the same diameter as that of the elongate cylindrical body ( 2 ) and comprises a flat ( 7 ) extending parallel to the axis of the cylindrical body over the main part of the cylinder body portion unoccupied by the thread. In a further embodiment, the screw-handling end ( 3 ) is formed with a plurality of flats ( 8 ) extending parallel to the axis of the cylinder body ( 2 ) at predetermined spacings. These flats extend over the main part of the cylindrical body portion unoccupied by the threadway and alternate with lands ( 9 ).

DESCRIPTION

[0001] 1. Field of the Invention

[0002] This invention broadly relates to a bone screw useful forfastening external splints, as applied to a fractured limb by orthopedicsurgery in order to stabilize the bone fracture.

[0003] In particular, the invention relates to a bone screw having anelongate cylinder body of predetermined length, a threaded end portionterminating with a tip, and an opposite screw-handling end.

[0004] 2. Prior Art

[0005] As it is well known in this specific technical field, one of themost effective methods for stabilizing bone fractures is based on theuse of external splints, whereby fractures at particularly delicatelocations, e.g. close to the joints, or fractures with attendant seriousinjury of the cutaneous tissue, can be set in all those cases in whichthe traditional plaster could be unsuitable or even impracticable.

[0006] Such splints are fastened at their opposite ends to respectiveundamaged portions of the broken bone, specifically to opposite sides ofthe fracture. The splint ends are fastened by means of bone screws whichare firmly implanted in the bone itself.

[0007] In the instance of a tibial fracture, for example, the oppositeends of a respective tibial external splint are fastened on either sidesof the fracture using appropriate bone screws. In other instances, whenthe fracture affects a joint, such as an ankle, the bone screws of arespective ankle external splint are implanted into the tibia and thetalus.

[0008] These bone screws are to provide reliable anchor points for theexternal splint device. To this aim, they generally comprise:

[0009] a screw shank, having a substantially elongate cylindrical shape;

[0010] a threaded screw portion, generally tapering toward a tip;

[0011] an opposite screw-handling end, that is a screw head structureand adapted for engagement by a driving tool, such as a wrench or apower driver.

[0012] Advantageously, the screw head consists of a short flat lyingportion, which is parallel to the screw axis and formed by a millingprocess at the screw end opposite to the tip.

[0013] In view of the bulky size of the above external splint apparatusand of its sticking out in the installed position from one side of thefractured limb, it will be appreciated that a splint device mayconstitute a bulky interfering attachment for both the operatingpersonnel and the patient. Accordingly, in this field it exists the needof reducing or at least of limiting such encumbrance.

[0014] A way of filling this demand is, for example, that of using bonescrews of different length and such that the ultimate implanted screwswill jut a shorter length out of the splint device.

[0015] For the purpose, the prior art provides each splint with aplentiful range of bone screws, all alike in shape and construction buthaving different lengths. Thus, the orthopedic surgeon will always havethe screw with the most appropriate length available for each case, andin the implanted state, the screw will not jut out of the splint device,although its handling end can still be easily reached.

[0016] This is a widely accepted and fairly satisfactory solution, butit can not fill the demands of every surgical situation. Besides, itstill exhibits technical shortcomings such as—perhaps mostimportantly—the difficulty represented by the need to select the bonescrew with the most suitable length “on the spot”, since once the screwimplanting operation is in progress using the selected screw, it isinconvenient or impossible to interrupt such operation to substitutesaid screw with a more suitable one. Because of the difficultyexperienced in selecting the screw with the most suitable length “on thespot”, it is not infrequent for one or more bone screws to jut outundesirably of the external splint after installation, resulting in theaforementioned drawbacks.

[0017] Another shortcoming is the large number of screws that must bemade available in order to cover the largest possible number ofoperative situations, which can occur. On the one side. this makes theselection less obvious, and on the other, weighs heavily on the overallcost for equipment.

[0018] FR 2 751 523 discloses a self tapping screw for fixingosteosynthesis plate. The screw comprises a self-tapping threaded shankwith a head connected by an intermediate brittle area to a gripping endto be inserted into the barrel of a screw driving tool.

[0019] U.S. Pat. No. 5,487,744 discloses a spinal fixation device forimmobilizing a portion of a spine which includes at least one spine rodand a plurality of bone screws that are threaded into an appropriatenumber of vertebrae and each of which includes a threaded end protrudingfrom the vertebra. Clamps are used to fasten a spine rod to the bonescrews.

[0020] EP 0729731 discloses a fixation system of column constituted by afitting of vertebral column, a pedicular stem which can be used in thecase of a traction as well as in the case of a fracture, a bolt screwprovided with a cylindrical recess, a nut and a cylinder shaped bar withflat exterior surface.

[0021] U.S. Pat. No. 4,778,388 discloses a root canal post for use inconstructing a therapeutic foundation on the root tooth for treatment ofa broken tooth, the post comprising a head, a shank and a bore axiallyproduced through the head and shank. The bore includes a fillerreleasably filled therein so that after the post is anchored in thetooth, a subsequent treatment for a possible secondary cavities isapplied through the bore which is made empty by removing the filler.

[0022] However, the heads of the screw according to FR 2 751 523 and thepost according to U.S. Pat. No. 4,778,388 have a diameter higher thanthat of their respective shanks, the bolt screw according to EP 0 729731 is to be allocated into a cylindrical hollow space of the fixationsystem and the screw according to U.S. Pat. No. 5,487,744 is providedwith two opposite threaded ends for anchoring the screw in a vertebraand for fastening the screw to the clamp respectively.

[0023] Due to the above characteristics, all the screws according to FR2 751 523, U.S. Pat. No. 4,778,388, EP 0 729 731 and U.S. Pat. No.5,487,744 have a fixed length and therefore display the sameinconveniences as those of the above-cited prior art screws.

[0024] U.S. Pat. No. 6,004,327 discloses a ratcheting compression devicewhich can be customized in length and comprises two pieces, of which oneis a pin comprising an elongate cylindrical body of predetermined lengthhaving located at or near its distal end a threaded portion and havingpreferably a substantially smooth portion at or near its proximal end.

[0025] However, although the threaded portion of the pin terminates witha tip, a substantial part of the above threaded portion has an outsidediameter which is higher than the diameter of the cylindrical body.

[0026] Furthermore, the pin is provided near its mid portion withratcheting means, preferably asymmetric teeth, which cooperate withanti-rotation means provided on the other piece of the device accordingto U.S. Pat. No. 6,004,327 in order to compress two segments of bonetogether.

[0027] The underlying technical problem of this invention is to contrivea bone screw with structural and functional features able to overcomethe aforementioned disadvantages. The invention devises a “universal”bone screw, which allows a substantially univocal selection of suchscrew in all types of external splint installations, and drasticallycuts down the expenses due to the necessity of requiring a comprehensiveset of screws which are similar in structure, but have differentlengths.

SUMMARY OF THE INVENTION

[0028] The principle of this invention is to have a handling end of thescrew of substantially the same diameter as that of the screw body andformed with a flat which extends over the main part of the screw body.

[0029] In an alternative embodiment, flats alternate with lands.

[0030] Based on this principle, the technical problem is solved by abone screw as previously indicated and characterized in claims 1 and 5.

[0031] The features and advantages of a bone screw according to theinvention will be apparent in the following description of an embodimentthereof, to be read with reference to the accompanying non-limitativedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the drawings:

[0033]FIG. 1 shows a perspective view of a bone screw according to theinvention;

[0034]FIG. 2 shows a perspective view of an alternative embodiment ofthe inventive screw;

[0035]FIGS. 3 and 4 are plan views of the screw shown in FIG. 1,respectively full length and as trimmed short;

[0036]FIGS. 5 and 6 are plan views of the screw shown in FIG. 2,respectively full length and as trimmed short;

[0037]FIG. 7 shows a perspective view of another embodiment of the bonescrew according to the invention;

[0038]FIG. 8 is an enlarged sectional view taken along lines VIII-VIIIof the screw shown in FIG. 7;

[0039]FIG. 9 shows a perspective view of a further embodiment of thebone screw according to the invention;

[0040]FIG. 10 is an enlarged sectional view taken along lines X-X of thescrew shown in FIG. 9.

DETAILED DESCRIPTION

[0041] Referring to the above drawings, a bone screw according to theinvention for fastening external splint apparatuses—as applied inorthopedic surgery to fractured limbs with the purpose to stabilize bonefractures—is generally shown at 1. Such splint apparatuses are not shownin the drawings since they are conventional.

[0042] The screw 1 has an elongate cylindrical body 2 of predeterminedlength. The body 2 has a longitudinal axis X-X and a circular section ofpredetermined diameter.

[0043] The body 2 tapers into an end portion 5 of the screw 1 which isthreaded and terminates with a tip 6.

[0044] An oppositely located screw-handling end, generally shown at 3,corresponds to the other free end of the cylindrical body 2. Thishandling end has substantially the same diameter as that of the elongatecylindrical body 2 and is essentially the head of the screw 1.

[0045] The elongate cylindrical body 2 of the screw 1 has a smooth mainportion 4, referred to as the shank of the screw 1 hereinafter.

[0046] Advantageously in this invention, the screw-handling end 3includes a flat 7 extending parallel to the axis X-X of said cylindricalbody 2. The flat 7 spans most of the portion 4 of the cylindrical body 2unoccupied by the thread 5, i.e. extends along the screw 1 shank.

[0047] The flat 7 is rectangular in shape, and in the example of FIG. 1provided on only one side of the screw shank, such as by a millingoperation.

[0048] The presence of the provided flat 7, allows to cut the shank ofthe screw at any location along the flat, as schematically shown in FIG.4, while maintaining a screw-handling end 3 always available. Tofacilitate the shank length trimming operation, a plurality oftransversal nicks 12 are formed in the cylindrical body 2 to mark thespots for cutting. Such nicks 12 are located at a predetermined distanceapart, e.g. provided at a spacing of 20 mm one from the other.

[0049]FIG. 2 shows a bone screw according to a second embodiment of thepresent invention. In the figures, the details of the bone screwsstructurally and functionally equivalents are indicated by the samereference numbers.

[0050] With reference now to FIG. 2, a bone screw 15 formed according tothe present invention includes a plurality of rectangular flats 8aligned with each other and at a predetermined distance apart one fromthe other.

[0051] These flats 8 alternate with lands 9, which practically establishthe distance separating the flats.

[0052] A flat 8 is joined to a separation land 9 by a radiused step.

[0053] The steps provided between flats 8 and lands 9 define abutmentshoulders for a tool, such as a T-wrench, employed to operate the bonescrew 1 from its handling end. This wrench is omitted from the drawingsbecause conventional.

[0054] The flats 8 are preferably the same length throughout. However,it would be possible for the flats 8 to have different lengths.

[0055] Advantageously, another plurality of flats 10 are formed in thecylindrical body 2 of the screw 15, correspondingly with anddiametrically opposite from said plurality of flats 8.

[0056] The flats 10 also alternate with separation lands 11.

[0057] More particularly, a separation land 9 of the diametricallyopposite plurality of flats 8 corresponds with a flat 10. Conversely, aseparation land 11 of the diametrically opposite plurality of flats 10corresponds with a flat 8.

[0058] The flats 10 and the respective separation lands 11 are alsojoined by a radiused step.

[0059] In the two embodiments of the invention shown in FIG. 7 and 9, inwhich details of the bone screws structurally and functionallyequivalents are indicated by the same reference numbers, bone screws 20and 30, formed according to the invention, include each a plurality ofsplines 21 extending parallel to the axis X-X of the cylindrical body 2and formed along the screw-handling end 3.

[0060] Particularly, in the embodiment shown in FIG. 7, bone screw 20includes four splines 21 which are in form of longitudinal grooves 22substantially angularly equally spaced.

[0061] In the embodiment shown in FIG. 9, bone screw 30 includes foursplines 21 which are instead in form of longitudinal facings 23substantially angularly equally spaced.

[0062] Splines 21, in particular longitudinal grooves 22 andlongitudinal facings 23, define in the handling end 3 of the screws 20and 30, respective splined shafts 25 in order to advantageously permit anon-rotating coupling between the screw and an adapter of a cuttingdevice, having, in its turn, a splined hole.

[0063] Merely as an example, the screw 1 may be an overall length of 240mm inclusive of a threaded portion 5, which is 80 mm long.

[0064] With a screw 240 mm long, the diameter of the shank 2 ispreferably 6 mm long, like the outside diameter of the threaded portion5 at the shank 2. The outside diameter of the threaded portion thentapers to 5.6 mm at the tip end 6.

[0065] Where the flat 7 stands an exceeding or unacceptable length outof the splint after the bone screw 1 of this invention is implanted, thescrew shank can be trimmed off by transversally cutting it at one of thenicks 12 of the cylindrical body 2. The clearance described by theprotruding shank can thus be significantly reduced, while it is stillpossible to turn the screw 1 for removal by engaging a flat 7 with theaforementioned T-wrench.

[0066] Advantageously in the second embodiment, the cut can be made atany of the flats 8 or 10. In fact, the section of the shank 2 to be cutthrough at the flats is smaller than the circular section, with either asingle longitudinal flat 7 or plural flats 8 being provided.

[0067] In fact, the radial thickness of the cylindrical screw body 2 isapproximately 5 mm when measured at a flat.

[0068] It should be noted, however, that this thickness reductiondoesn't significantly lower the breaking point of the screw under a hightorque.

[0069] Thus, the invention solves the technical problem by providing auniversal bone screw effective to reduce the need to maintain a set ofdifferent length bone screws.

[0070] A major advantage is a minimized clearance outline for the splintdevice.

[0071] Another advantage becomes evident at the splint installing stage,when the orthopedic surgeon is no longer to make decisions about thescrew size since he can use a single screw type to trim depending on thenecessity.

[0072] A further advantage is that cutting the shank is facilitated bythe reference marks represented by the nicks or by the radiused steps.Furthremore, cutting can be advantageously performed by means of acutting device of the type having an adapter with a splined hole whichcan be coupled to a corresponding splined shaft formed on the screw.

[0073] Finally, the screw of this invention can be manufactured withlarge-volume methods.

1. A bone screw, particularly for use with external splints in fracturestabilization, comprising an elongate cylindrical body (2) ofpredetermined length and diameter tapering into a threaded end portion(5) which terminates with a tip (6), and an opposite screw-handling end(3), characterized in that said screw-handling end (3) has substantiallythe same diameter as that of the elongate cylindrical body (2) andcomprises a flat (7) extending parallel to the axis of said cylindricalbody (2) over the main part of the cylindrical body portion unoccupiedby the threadway.
 2. A bone screw according to claim 1, characterized inthat said cylindrical body (2) comprises a plurality of transverse nicks(12) at predetermined spacing to mark out lines of cut.
 3. A bone screwaccording to claim 1, characterized in that said flat alternates withlands.
 4. A bone screw according to claim 1, characterized in that saidflat (7) is rectangular in shape.
 5. A bone screw according to claim 1,characterized in that it comprises a plurality of splines (21) extendingparallel to the axis of the cylindrical body (2) and formed along thescrew-handling end (3).
 6. A bone screw according to claim 5,characterized in that said splines (21) are in form of longitudinalgrooves (22).
 7. A bone screw according to claim 5, characterized inthat said splines (21) are in form of longitudinal facings (23).
 8. Abone screw, particularly for use with external splints in fracturestabilization, comprising an elongate cylindrical body (2) ofpredetermined length and diameter tapering into a threaded end portion(5) which terminates with a tip (6), and an opposite screw-handling end(3), characterized in that said screw-handling end (3) has substantiallythe same diameter as that of the elongate cylindrical body (2) andcomprises a plurality of flats (8) extending parallel to the axis ofsaid cylinder body (2) at predetermined spacing over a main portion (4)of the cylindrical body portion (2) unoccupied by the thread (5) andalternating with separation lands (9).
 9. A bone screw according toclaim 8, characterized in that another plurality of flats (10)corresponds, at an angularly shifted location on said cylinder body (2),to said plurality of flats (8).
 10. A bone screw according to claim 8,characterized in that another plurality of flats (10) corresponds, at adiametrically opposite location on said cylinder body (2), to saidplurality of flats (8).
 11. A bone screw according to either claim 9 or10, characterized in that a flat (8) corresponds to a separation land(11) of said another plurality of flats (10) formed at angularly shiftedor diametrically opposite locations.
 12. A bone screw according to claim8, characterized in that said flats (8) are rectangular in shape andhave the same dimensions.
 13. A bone screw according to claim 9,characterized in that said flats (8) are joined to said lands (9) by aradiused step.
 14. A bone screw according to claim 8, characterized inthat it comprises a plurality of splines (21) extending parallel to theaxis of the cylindrical body (2) and formed along the screw-handling end(3).
 15. A bone screw according to claim 14, characterized in that saidsplines (21) are in form of longitudinal grooves (22).
 16. A bone screwaccording to claim 14, characterized in that said splines (21) are inform of longitudinal facings (23).